Protection of electric apparatus



PROTECTION OF ELECTRIC APPARATUS Filed June 28, 1927 Patented June 18, 1929'.

PATENT oFFicE.

IAX BUCHHOLZ, F CASSEL, GERMANY.

PROTECTION l' ELECTRIC APPARATUS.

Application led June 28, 1927, Serial No. 202,143, and in Germany July 1, 1926.

My invention refers to electrical apparatus "of all kinds and more especially to means whereby such apparatus can be protected against partial or totalv destruction by overloads caused by excess currents, short circuits and the like. It is an object of my invention to provide means whereby the detrimental effect of such overloading of current carrying parts is prevented from influencing such parts either by cutting same out before any injury has been done them or by setting some annunciating device in operation to warn the attendant.

As is well known to those skilled in the art,

when electrical transformers, switches or other' electrical apparatus are overloaded by short circuits,- excess currents and the like,

the current carrying parts will be unduly heated2 and if insulating means are provided -adjoining such parts, vapours or gases of decomposition of the solid or fluid insulating means will be developed after some time around the current carrying parts. It is equally known that these gases or vapours aire more dangerous even than air bubbles, inasmuch as t ey embody iinely distributed solid products of decomposition, such as for instance soot, which are conductive and are therefore liable to create leakage paths and the like. For practical reasons an exhausting ofthe gases thus formed is frequently impossible and such step would only constitute an imperfect remedy inasmuch asthe solid Eroducts of decomposition would not be exausted along with the gases. In consequence of these circumstances the insulation of the current car ing parts will gradually be diminished in va ne and it is therefore imperative to prevent gases or vapours of deof com osition from being developed. In other wor s, provision must be made for preventi the current carrying arts and their insu ation from being overo aded so as to prev ent at the same time the decomposition of the insulating means.

' According to the present invention this is attained by a protective system comprising a protective conductor electrically connected with the current carr ing parts to be protected, either in parallel or in series or in mixed connection, thisprotective conductor being arranged or formed in such manner as to have its temperature changed by an overload, which may occur in the system, before the temperature of thecurrent carrying parts to be protected is changed. The temperature of the said protective conductor will there-. fore also overstep at an earlier moment the limit at which a decomposition of the surrounding solid or liquid insulating material or the formation of gases or vapors from this material begins. Therefore, if the protective conductor is subjected to an overload, gas or vapor bubbles will be developed in the insulating material in contact with the said conductor, before such development can take place at the other current carrying parts, and these gas or vapor bubbles will operate a protective device provided for this purpose, which may be a mechanical or electrical interrupting device or some annunciating device or alarm, thereby providin that the current carrying part is cut out be ore any harm is done. Accordin to my invention I cause 'the protective con uctor to cooperate with fluid or solid media surroundin same, for instance with the insulatin liquid such as oil, carbon tetrachloride or t e like or with solid insulating means in such manner that the gases or vapours developed from such media, either by evaporation or by decomposition, brought about by the rise of temperature in the conductor, are caused to act on the electrical or mechanical protective device provided for this purpose so as to either cut out the part to be protected or to actuate a mechical or electrical annunciatin device.

In the drawings ailixed to t is specification and forming part thereof two arrangements embodying my invention are illustrated diagrammatically by way of example, Fig. l being a vertical section of a three-phase transformer provided with protective means embodying my invention while Fig. 2 shows the invention. as applied to a cable or bus bar.

Referring iirst to Fig. l, a is the transformer tank filled with an insulatin liquid such as oil, b is the compensating tan and c is the pipe connectin same. The three phases d1 d2, d, extend t rough inlet bushes e1, e2, e3, into the tank a and arev connected to the three transformer coils f1, f, f. In order now to prevent gases or vapours of decomposition of the oil or other insulating medium to be formed at the coils f1, f2, f, in the case of an overload in the system, a protective conductor is inserted between the inlet bush e2 of the p ase d2 and the coil f2. In the modiiication illustrated in the drawing, th'is protective conductor has a helical form and can for instance consist of solid copper wire of circular cross section, this section being somewhat smaller than the cross section of the copper wires in the coils. In consequence of this the manner described in my co-pending. ap'

plication for patent of the United States,

filed September 15, 1922, Serial No. 488,457

and ythe divisional ap lications` resulting therefrom. To this en some suitable protective device, for instance a contact of a protective circuit may be disposed in the case k inserted in the pipeV c leading from the transformer tank a to t-he compensating vessel b, this contact being operatedeither by an excess pressure caused by the gases developed in the oil or b the buoyancy eli'ect of these gases, as they rise in the liquid and in the pipe c or by their catalytic action or by other causes. The contact being thus actuated by the gases developed at g will then either cut out the transformer altogether or will operate an annunciating device, for instance,

an alarm., fo'rrning part of the protectivel circuit. l

Obviously the formation of ases or vapours at the transformer coils t emselves is alto ther prevented and there is noneed for emp oying the well known complicated overload rel and the like.

If desired, the protective conductor, such as g, can be surroundedby heat insulator, such as .for instance paper, cotton, asbestos or the like, in order .to better utilize the rise of temperature` in vthis conductor and to accelerate the formationlo gases.

I may also use a rotectiveconductor consistin of a materialwhich is heatedup more quick y than the material forming art'of the other current carrying-parts, there y causing the formation of vapours or gaseous productsV of decomposition in the medium surrounding the protective conductor, before the other current carrying arts are affected. In the manner' escrib'ed with reference toa transformer also all other electricaldevices and apparatus can be protected, such as sw1tches,generetors, motors, cables, bus bars and the like.. l v l In Fig. 2 a cable embodying my invention is lllustrated'. z' is the electrical conductor forming part of the cable and k is the insulation surrounding same. tive conductor of smaller cross section than the cable conduct'r which is inserted in the same and is enclosed in an asbestos envelope Z, the Whole bei Surrounded by a fluid insulating mediumfigor instance oil, contained in a sleeve ym. The sleeve m has T-shape, an extension o being formed thereon, in which is mounted an electrical contact device forming part of a. protective circuit and having the form of a plate-shaped lever p pivoted to the Wall of the extension 0 for free rocking motion in vertical' direct-ion. Vi'henever an overload occurs in the cable, the insulation l. and the oil surrounding the protective conductor i willbe decomposed long beforethe cable conductor z' is unduly overloaded and the gas bubbles formed at z" will rise in the oil and in collecting below the rocking plate p vwill lift same so as to close the contact and the'4 protective circuit.

-The term protective device asused -in the claims here annexed is to be understood' to include mechanical' as well as electrical means for automatically cutting out the'system to be protected or for operating'an annunciatingz' device of some suitable kind.

I wish it to be understood that I'do not desire to-be limited -to the exact details of construction'shown and described for obvious 'i modifications will occur-to a personr Skilled in the-art i l.

1. Protective system for electrical' devices comprising a current carr ling part, a' protective conductor electrical 'y connected with said part, a non-gaseous insulator in contact with said conductor, said conductor being adapted to 'have its physical condition changed before the physical condtion'of said part is changed, an adapted toY be set operating by prodncts'of decomposition from said'insulator devel ed in consequence of such change in'said con c4' tor, for varyin the operative condition 'of said rotective evice. 2. rotective system for electrical devices tective conductor electrical connectedwith said part, nonvaseous insu atin meansv decomposable by heat in contact with'saidconl ductor, said conductor bein ada its temperature changed ture of said part is changed, and aprotectiv'e"V deviceadapted to be set operatialvigby procomprising a current carring part, a` prod ucts of decomposition from s'aid'-insulatingl a protective ldevice' i is a protecsus4 ted to have be ore t e tempera-v means developed in 'consequence gf suc Y. change in said conductor, fm` val-ym? me, IPT

erative condition of said protective evce.

3. AProtective system forelectrical devices comprising a current carr 'ng part,a rot'e'c tive conductor electrica y connecte with said part, non-gaseous insulatin meansldecomposable by heat in contact with said coni its temperature changed be n ture of said part is changed, a protective cir-- ductor, said conductor bein ada. ted to have ore t e temperacuit and a contact in said circuit ada ted to be operated by products of'decomposition of said insulating means. i

4. Protective system for electrical devices comprising a .current carrying part, a, conductor ofsmaller cross-sectional area inserted in said part, non-gaseous insulating medium in contact with said conductor, a vprotective circuit and a contact forming artof said circuit and adapted to be actua by the products resulting from a rise of'temperature in said insulating medium.

5. Protective system for electrical devices comprising a current car ing part, a conductor of mnaller cross-sectional area inserted in said part, non-gaseous insulating medium i in contact `with said conductor, a protective 20 

